This invention is concerned with the field of internal combustion engines employing electronic ingnition. More particularly, the invention relates to an electronic system for igniting the air-fuel mixture injected into the cylinders of an internal combustion engine and, more precisely, to a system of this type which enables the principal mechanical components (contact breaker, distributor, centrifugal advance, etc. . . . ) to be eliminated and which is capable of automatically supplying ignition signals at a precise instant in all the operating modes of the engine and in accordance with the measured parameters of state which are the most representative of these various modes of operation.
Conventional ignition systems, i.e. the ignition systems found in almost all existing combustion engines, typically comprise one or more mechanical contact breakers which control the current passing through the primary winding of an ignition coil in which electrical energy is stored and then released, inducing a very high voltage in the secondary winding of this coil. This very high induced voltage is transferred to the spark plugs through a rotary mechanical commutator commonly known as a distributor.
The various disadvantages attending mechanical contact breakers are well known: erosion of the contacts, deposition of troublesome films, inertia, inherent frequency and contact bounce. The very high voltage distributor is also affected by erosion phenomena and also shows high susceptibility to the ambient conditions. In addition, these conventional ignition systems comprise other mechanisms which are necessary for varying the instant, i.e. the angle, of ignition of the cylinders in dependence upon the operating modes of the engine. These mechanisms are commonly known by the names of "centrifugal advance" and "vacuum correction".
In order to remedy the above mentioned deficiencies of conventional ignition systems, various solutions have been proposed. Some of these solutions have been developed and recently brought into service. They include the "electronic igniters" or spark generators in which the mechanical contact breaker has been eliminated and replaced by solid-state components. Spark generators such as these are at present marketed in two forms, namely coil ignition and ignition by a condenser associated with a step-up transformer.
Although electronic solutions have been proposed in the field of devices for correcting advanced and retarded ignition, their correct operation throughout all the service modes of the engine is often not precise enough and is susceptible to parasitic electrical disturbances. The means necessary for ensuring correct operation of these devices are generally onerous and, as a result, their adoption for practical use has been retarded.
More recently, in the field of distributors, it has been proposed to use spark generators which are sequentially triggered by the electrical signals supplied by an electronic commutator formed by a programmable counter fed by an electrooptical transducer. The present invention seeks to obviate the above-mentioned disadvantages.